The Confusion About Bright Line Spectra

Niels Bohr – Danish physicist, working for Thomson (raisin bun guy) suggested that line spectra could be explained using ideas from the quantum theory!

Bohr began to work with Rutherford (1913) – modified Rutherford’s atomic theory

Bohr’s Model of the Atom

54 years after line spectra were first described qualitatively by Bunsen and Kirchhoff.

28 years after line spectra were described quantitatively by Jacob Balmer.

Bohr’s Postulates

The atom has only specific allowable energy levels (stationary states) & each stat.state corresponds to the e-s occupying fixed circular orbits around nucleus.

While in stat.state, atoms do not emit energy.

An e- changes stat. state by emitting or absorbing a specific quantity of energy that is exactly equal to the difference in energy btw the two stat. states. (Fig 4/176)

Higher energy level -> lower: loss of energy in the form of light

Lower energy level -> higher: energy is absorbed

Only certain quanta of light can be emitted or absorbed by an atom, so the energy of the electrons inside the atom is also quantized. In other words, an electron can only have certain allowable energies. (staircase analogy).

H-spectra example

If an e- that has been excited to the 3rd NRG level & then falls from 3rd to 2nd NRG level, emits a photon of red light with wavelength 656nm & red line is visible on emission spectrum.

Each line on e. spectrum corresponds to a specific energy transition (I.e. 4th to 2nd = green, 5th to 2nd = blue)